A double facer incorporated in a corrugator uses a gluing device that applies glue to the flute tips of a single faced corrugated cardboard, which is formed by gluing a medium web with a bottom linerboard, so that the single faced corrugated cardboard is glued with a top linerboard.
The gluing device deposits glue stored in a glue bath onto a gluing roll and adjusts the glue on the gluing roll to a predetermined thickness using a doctor roll. After that, the device passes a single faced corrugated cardboard through a nip between the gluing roll and a pressure roll, and transfers the glue on the gluing roll to the flute tips of the single faced corrugated cardboard while passing through the nip.
Normally, an amount of glue to be applied to a single faced corrugated cardboard is adjusted by the space between the gluing roll and the doctor roll. Alternatively, the amount of glue to be applied can be adjusted by adjusting the number of flute tips being concurrently in contact with the gluing roll. Specifically, more flutes being concurrently in contact increases an amount of glue to be applied to each flute tip. The number of flutes being in contact with the gluing roll at the same time is practically three or so.
If an excessive amount of glue is applied to flute tips of a single faced corrugated cardboard, the portion applied excessive glue to excessively shrinks after the applied glue is dried and the flatness of the resultant single faced corrugated cardboard is not maintained. An optimum amount of glue to be applied to each flute tip is different with the basic weight of the paper web or the flute shape (flute type) of a single faced corrugated cardboard as well as the traveling speed of the single faced corrugated cardboard.
Patent Literature 1 discloses means for changing the number of flutes being concurrently in contact with the gluing roll, so that an optimum amount of glue can be applied in accordance with the traveling speed of the single faced corrugated cardboard. Hereinafter, description will now be made in relation to a method of gluing disclosed in Patent Literature 1 with reference to FIG. 4(a) and FIG. 4(b).
A gluing device 100 of the double facer in FIG. 4(a) and FIG. 4(b) includes a glue bath 102 containing glue g; a gluing roll 104 having a lower part immersed in the glue g; a doctor roll 106 disposed above the surface of the glue g; and a pressure roll 108 forming a nip N between the gluing roll 104 and the pressure roll 108.
A single faced corrugated cardboard k manufactured in a single facer that is disposed upstream of the double facer is heated by a non-illustrated preheater, then travels in the direction of the arrow a to be wrapped around the pressure roll 108, and enters the nip N between the gluing roll 104 and the pressure roll 108. Flute tips m of the single faced corrugated cardboard k wrapped around the pressure roll 108 are applied with glue g adhering to the surface of the gluing roll 104.
In FIG. 4(a), if a casing 110 that supports the gluing roll 104 and the doctor roll 106 is moved in the direction of arrow b using a non-illustrated driving device, two or more (e.g., four) flute tips m of the single faced corrugated cardboard k come into contact with the gluing roll 104. This makes it possible to surely apply glue g to the flute tips of the single faced corrugated cardboard k even the double facer is running at a high speed.
In FIG. 4(b), if the casing 110 is moved in the direction of arrow c while the single faced corrugated cardboard k travels at a relatively low speed, only one flute tip of the single faced corrugated cardboard k, for example, comes into contact with the gluing roll 104, so that, according to Patent Literature 1, an excessive amount of glue g is not applied even during low-speed operation.
Furthermore, Patent Literature 1 states that: since the single faced corrugated cardboard k which is leaned to be flat in the width direction is wrapped around the pressure roll 108, the single faced corrugated cardboard k can be free from warp and can be applied glue film uniformly in the width direction. Also, Patent Literature 1 states that the pressure roll 108 may be moved forwards or backwards in the directions of arrows b and c in place of the gluing roll 104.